Contents

The discovery that 2001 QC298 is a possible binary TNO was announced
in IAUC 8034 by Noll et al.. The object appears elongated in four
HST/NICMOS images, with image analysis suggesting two components with
separation of arcsec ( km).
IAUC: http://cfa-www.harvard.edu/iauc/08000/08034.html

There were 34 new TNO discoveries announced since the previous issue of
the Distant EKOs Newsletter:

We examine possible locations for the primordial disk of the
Edgeworth-Kuiper Belt (EKB), using several subsets of the known
objects as markers of the total mass distribution. Using a secular
perturbation theory, we find that the primordial plane of the EKB
could have remained thin enough to escape detection only if it is
clustered very closely about the invariant plane of the Solar System.

In this paper we report numerical simulations of the dynamical evolution
of the region a>50 AU. We found that some dynamical effects such as
high-order secular resonances with the rate of precession of Neptune's
node of the form
with k=4,5,...
or combined mean motion resonances with Uranus and Neptune of the form
may spread a very thin primordial disk in
this region after 4.5 Gy of evolution by a factor of up to 2.

We study the effects of a Mars-like planetoid with semimajor axis at
about 60 AU orbiting embedded in the primordial Edgeworth-Kuiper
Belt (EKB). The origin of such an object can be explained in the
framework of our current understanding of the origin of the outer
Solar System, and a scenario for the orbital transport mechanism to
its present location is given. The existence of such an object would
produce a gap in the EKB distribution with an edge at about 50 AU,
which seems to be in agreement with the most recent observations. No
object has been detected so far at low eccentricities with semimajor
axes beyond 50 AU, even though, the present observing capabilities
would allow an eventual detection (Gladman et al. 1998, Jewitt
et al. 1998, Chiang et al. 1999, Allen et al. 2000,
Trujillo et al. 2001, Gladman et al. 2001a, Trujillo and
Brown 2001). Finally, ranges for the magnitude and proper motion of
the proposed object are given.

I simulate the orbital evolution of the four major planets and a
massive primordial planetesimals disk composed of 104 objects,
which perturb the planets but not themselves. As Neptune migrates by
energy and angular momentum exchange with the planetesimals, a large
number of primordial Neptune scattered objects are formed. These
objects may experience secular, Kozai and mean motion resonances that
induce temporary decrease of their eccentricities. Because planets are
migrating, some planetesimals can escape those resonances while in a
low eccentricity incursion thus avoiding the return path to Neptune
close encounter dynamics. In the end, this mechanism produces stable
orbits with high inclination and moderate eccentricities. The so
formed population together with the objects coming from the classical
resonance sweeping process originate a bimodal distribution for the
Kuiper Belt orbits. The inclinations obtained by the simulations can
attain values above and their distribution resembles a
debiased distribution for the high inclination population coming from
the real classical Kuiper Belt.

We report several results related to the dynamical evolution of dust
produced in the Kuiper Belt (KB). We show that its particle size
frequency distribution in space is greatly changed from its
distribution at production, due to the combined effects of radiation
forces and the perturbations of the planets. We estimate the
contribution of KB dust to the zodiacal cloud by calculating its
number density radial profile near the ecliptic. We also study the
contribution of KB dust to the population of IDPs collected at Earth,
by calculating geocentric encountering velocities and capture rates.
Our models show, in contrast with previous studies, that KB dust
grains on Earth-crossing orbits have high eccentricities and
inclinations, and therefore their encountering velocities are similar
to cometary grains and not to asteroidal grains. We estimate that at
most 25% in number of captured IDPs have cometary or KB origin;
the KB contribution may be as low as 1-2%. We present the velocity
field of KB dust throughout the Solar System; this, together with the
number density radial profile, is potentially useful for planning
spacecraft missions to the outer Solar System.

Near-infrared spectra of Centaur 8405 Asbolus have been obtained,
covering the whole rotational period. Complementary photometry and
visible spectroscopy have also been performed. The aim of this project
was to confirm or refute the water ice detection on one side of
Asbolus reported by Kern et al. (2000 Astrophys. J., 542,
L155-L159). We found no absorption feature at any rotational phase of
Asbolus. Our study is the first in-depth investigation of a centaur
over a complete rotational period. Our results seem also to indicate
that a change in the slope from 0.8 to 1.0 m may occur in Asbolus
spectrum.

We describe the results of a ground-based observational ``snapshot''
study of Jupiter-family comets in the heliocentric range 2.29 AU 5.72 AU. Results are presented based on observations from
the 1m JKT on the island of La Palma. A total of 25 comets were
targeted with 15 being positively detected. Broad-band VRI photometry
was performed to determine dimensions, colour indices, and dust
production rates in terms of the ``Af'' formalism. The results for
selected comets are compared with previous investigations. Ensemble
properties of the Jupiter-family population have been investigated by
combining the results presented here with those of Lowry et
al. (1999), and Lowry & Fitzsimmons (2001). We find that the
cumulative size distribution of the Jupiter-family comets can be
described by a power law of the form
. This size distribution is considerably shallower than that
found for the observed Edgeworth-Kuiper belt objects, which may
reflect either an intrinsic difference at small km-sizes in the belt,
or the various processes affecting the nuclei of comets as their
orbits evolve from the Edgeworth-Kuiper belt to the inner Solar
system. Also, there would appear to be no correlation between nuclear
absolute magnitude and perihelion distance. Finally, for the sample
of active comets, there is a distinct correlation between absolute R
band magnitude and perihelion distance, which can be explained by
either a discovery bias towards brighter comets or in terms of
``rubble'' mantle formation.

Based on astrometry from an orbit derived by HST imagery, Charon's
orbital eccentricity has been reported to be in the range of
0.003-0.008 (Tholen & Buie 1997, Icarus, 125, 245). Solar and
planetary tides are orders of magnitude too small to induce the
reported eccentricity (Weissman et al. 1989, GRL, 16, 1241). This
non-zero value, if correct, therefore indicates some significant
forcing against the two-body tidal equilibrium value, which should
formally be zero. Here we follow up on a preliminary study (Levison &
Stern 1995, LPSC, 26, 841) to investigate whether the reported
eccentricity of Charon's orbit could be due to gravitational
perturbations by KBO flybys through the Pluto-Charon system and KBO
impacts directly onto Pluto and Charon. We find it is unlikely that
Charon's reported eccentricity could be caused by this
effect. Although we cannot rule out some additional source of
eccentricity excitation (e.g., an undiscovered satellite in the
system, or a Kozai resonance), our analysis indicates it is plausible
that Charon's actual orbital eccentricity is substantially smaller
than the 0.003 lower limit reported previously.

The observed transneptunian binaries, with components of comparable
mass and large separations, cannot be the result of collisions in the
present dynamical environment of the Kuiper belt. They could be
produced by collision of two planetesimals within the sphere of
influence of a third body during low-velocity accretion in the solar
nebula. Thus, they are primordial.

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